Guitarists need instrument amplifiers capable of producing new sounds as well as high-quality approximations of signature vintage amplifier tones. Historically speaking, original vintage equipment was often under-powered, which led to the practice of turning them up to maximum volume in order to fill the room with sound. Under these operating conditions, vintage amplifiers would often distort the signal, which guitarists found beneficial to the sound quality. This created a problem for the musician, namely, how to achieve a distorted sound at lower volumes. The prior art is filled with numerous approaches to satisfy the guitarist's need for tube amplifier sound at moderate and low sound pressure levels:
In U.S. Pat. No. 6,140,870, a tube amp feeds solid-state power output section to achieve the desired sound.
In U.S. Pat. No. 4,937,874, signal conditioning is used to create a compensated output for further amplification.
In U.S. Pat. No. 5,268,527, a solid-state amp with tube amp impedance matching is utilized.
In U.S. Pat. No. 5,550,509, the output section screen voltage is reduced to control the overall volume levels.
In U.S. Pat. No. 5,727,069, a solid-state amp with tube limiting is utilized.
In U.S. Pat. No. 6,111,961, a dummy load is utilized to reduce the signal levels.
In U.S. Pat. No. 5,635,872, an adjustable power supply sag and distortion approach is utilized.
In U.S. Pat. No. 8,155,348 B2, an external phase inverter anode voltage regulation apparatus is utilized.
The problems associated with all of these various methods include complex circuitry and associated higher manufacturing costs, undesirable changes in the sound quality and/or the sensitivity or “dynamic feel” of the amplifier, as well as confusing user interfaces. Even something as simple as two knobs often requires the customer to figure out a complicated process to achieve an acceptable sound.
Each of the various approaches to reducing overall volume have some measure of limited effective operating range such as 10-20%. While it is possible to reduce the perceived volume level in most cases all the way down to “zero” sound, the perceived sound and feel of the amplifier worsens at settings beyond this range. This may be due to reliance on one “magic-bullet” approach, concept or circuit to do all of the work necessary to reduce the volume.